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One of the most revolutionary things we learned in the 20th century was that time is not absolute
20世纪，我们所了解到的最具变革性的事情之一就是，时间不是绝对的，
– the rate at which time passesis different
时间流逝的速度是不同的，
depending on how fast you're moving and how much you're accelerating.
这取决于你移动和加速的速度。
In particular: time passes slower the more you're moving.
特别是：你运动得越快时间推进得慢越。
This fact has been confirmed experimentally countless times – fast-moving muons take longer to decay,
这一事实已被无数次实验确认——快速移动的u介子需要更长的时间衰变，
light emitted from a moving source has a lower frequency, and so on.
从一个运动的光源发出的光频率更低，等等。
But relativity of time can at first glance seem somewhat contradictory.
但乍一看，时间的相对性似乎有些矛盾。
Suppose we're flying past each other; from my perspective it seems like you're moving
假设我们正在飞过对方；从我的角度看，好像你正在移动
(and so time should go more slowly for you), and from your perspective
（所以时间你来说应该推进得更慢），从你的角度看，
it seems like I'm moving (and so time should go more slowly for me).
好像是我正在移动（所以时间对我而言推进的更慢些）。
It seems crazy that we can both think time is going slower for the other person – someone's time must actually be slower, right?
我们都觉得对方的时间要慢些，这似乎很有点疯狂——其中一定有一个人的时间推进是更慢的，对吧。
Well, no - take a look at my giraffe. It's 3 meters tall. And your giraffe is 3 meters tall, according to you.
不是的——看看我的长颈鹿，高3米。你的长颈鹿，在你看来高3米。
But you're rotated relative to me, so you only measure my giraffe to be 2 meters high.
但是你是相对于我旋转的，所以你测量我的长颈鹿只有2米高。
And I'm rotated relative to you, so I only measure your giraffe to be 2 meters high.
并且我相对于你是旋转的，所以我测量你的长颈鹿，也只有2米高。
So we each think the other is measuring distances in space as longer, but it's not a contradiction.
因此，我们都认为对方测量的空间中的距离较长，但这并不矛盾。
It's just that we've rotated height and width relative to each other.
这只是我们相当于彼此旋转了高度和宽度。
And similarly, when you change your speed, you rotate the direction of time – I have another video explaining why.
同样，当你改变你的速度时，你也旋转了时间的方向——我们的另一期视频可以解释原因。
But it looks like this: if every passing second I move to the left, then my clock will tick like this.
但它看起来是这样的：如果每一秒我都向左运动，那么我的时钟会像这样运转。
And if every passing second you move to the right, then your clock will tike like this.
如果你每一秒都向右运动，那么你的时钟会像这样运转。
So when three seconds have passed on my clock, I'll measure only two seconds having passed for you.
所以，当我的时钟走过了3秒，我将测量出，对你来说时间只过了2秒。
And yet when three seconds have passed on your clock, you'll measure only two seconds having passed for me.
但当你的时钟走过了3秒，你会测量出，对我而言，时间也只过了2秒。
So we each think the other is measuring distances in time as shorter, but it's not a contradiction,
因此，我们都认为对方测量的时间更短，但它并不矛盾，
it's just how time behaves when it's rotated – it affects not just the passage of time, but also our notions of 'the same time'.
当时间旋转之后就会这样——它不仅影响了时间的流逝，也影响了我们对于“同一时间”的概念。
However, there's still an unanswered question: what if I stay on earth and you go off into space and then come back?
但还是有一个悬而未决的问题：如果我留在地球上，你出发去往太空，然后再回来，会发生什么？
Will one of us have actually aged more, or will we both have aged the same amount despite constantly thinking the other was aging less?
我们中的一个将会变老更多吗，还是我们将会衰老同样的年纪，尽管人们总是认为其中一个会衰老得更少？
This conundrum is called the Twins Paradox, and I'll explain the solution to it in my next video.
这个难题被称为双胞胎悖论，我会在我的下一个视频中解释它。
But in the meanwhile, can you use rotating time to figure out why the twins paradox isn't a paradox?
但是在此期间，你可以用旋转时间弄清楚为什么双胞胎悖论不是一个悖论吗？
